I agree. If they were concerned about the trial,
Post# of 148301
To me, the fact that they "wanted" to look at 42 day data at the 75% mark was an indication that they thought they may be able to halt the trial at 75%.
Obviously this is my biased opinion. Its possible that they wanted to review/ammend the PE and/or trial size at 75%.
I just think its more likely that they would have recommended the change at 50%, because that was the express purpose of the 50% interim.